Hitherto, there has been known as a material to absorb vibration energy, such as a vibration damping material, soft vinyl chloride resins formed of a vinyl chloride resin added with a plasticizer. The soft vinyl chloride-based resins are designed so as to attenuate the vibration energy by consuming the vibration energy in the resins as frictional heat. However, the absorption and attenuation of the vibration energy is still insufficient.
Besides, rubber materials such as butyl rubber and acrylonitrile-butadiene rubber have been widely used as the vibration damping materials, which are excellent in terms of processability, mechanical strength, and costs. However, though those rubber materials are most excellent in attenuation performance (transfer-insulating or transfer-reducing performance of vibration energy) among the general polymeric materials, the vibration damping ability (absorbability of vibration energy) thereof is too low for its sole use as the vibration damping material. Therefore, to apply the rubber materials, for example, to vibration proof structures for buildings or apparatuses, the rubber materials have been used in composite forms such as a laminate of the rubber material and a steel plate and a vibration damping structure of the laminate combined with a lead core that absorbs vibration energy by plastic deformation or an oil damper.
Thus, the conventional rubber materials cannot be solely used as the vibration damping materials as described above, and should be made into composite forms, inevitably making the vibration proof structures complicated. As a result, it has been demanded to enhance the vibration damping ability of the vibration damping materials themselves and the rubber materials themselves.
There are disclosed compositions formed mainly of a polymeric material and a piezoelectric powdery material (JP 03-188165 A, and Inaba, et al., “Relationship between Mechanical Properties and Damping Performance of Piezoelectric Damping composites,” Journal of The Society of Rubber Industry, Japan, vol. 67, p. 564 (1994)). Those compositions are intended to absorb and attenuate vibrations by converting vibration energy into electric energy by the action of electro-mechanical conversion of the piezoelectric material and dispersing the electric energy. However, to achieve a sufficient effect, the compositions must contain the piezoelectric particles in an amount as large as 50% by mass or more. The blending in such a high content lowers the fluidity in a molten state and makes the kneading and molding difficult. In addition, since the piezoelectric particles are made of ceramics such as lead zirconate titanate and barium titanate, the composition is increased in its mass, which being a drawback.
There has been disclosed a vibration damping material including a polymer matrix that contains an active ingredient for increasing dipole moment (Inoue, et al., Damping Behaviors of Chlorinated Polyethylene/N,N′-dicyclohexyl-2-Benzothiazole Sulfenamide Organic Hybrid: Journal of The Society of Fiber Science and Technology, Japan, vol. 56, p. 443 (2000)). However, since the active ingredient used in the material is a low-molecular compound, the material has such a drawback that the active ingredient exudes from the polymer matrix to deteriorate the performances.
There have been known vibration damping materials including a polymeric material such as a polyester resin or the like, and an electroconductive material. For example, JP 2003-221496 A discloses a vibration damping material in which a polyester resin is used as the polymeric material and the electroconductive material is dispersed, but has no description about the use of a specific polyester resin. JP 2003-221496 A describes a composite vibration damping material made of a viscoelastic resin including a copolyester, a crosslinking agent, etc. Accordingly, the production of the composite requires a step of crosslinking reaction by heating. Thus, the production method disclosed in JP 2003-221496 A cannot be said necessarily simple and easy. Further, the glass transition temperature of the copolyester, which can be used herein, is limited to fall within a range of from −60° C. to 0° C., so the material does not necessarily fully satisfy the requirements as the material being excellent in versatility.
Further, JP2003-241766 A relates to a sound damping structure using nonwoven fabric for a polyester resin or the like, JP2003-171820 A relates to a sound damping fiber using a piezoelectric polymer for the polyester resin or the like, and JP 5-222239 A relates to a vibration damping steel sheet using a viscoelastic resin for the vibration damping materials for the polyester resin or the like. However, the specific descriptions of the components constituting the polyester resins are not made in those documents.
Further, there is disclosed a resin composition formed of a polymeric material and a filler. However, there is not disclosed a vibration damping material prepared by incorporating fillers into a polyester resin in which the ratio of carbon atoms in a polyester main chain is specified. JP 10-67901 A relates to a thermoplastic polymer composition using styrene resins. JP 10-231385 A relates to a composition for a vibration damping material containing polyvinyl chloride, chlorinated polyethylene, and epoxidized polyisoprene. However, those compositions are not necessarily high in vibration damping ability despite that a sample piece has a relatively large thickness of 2 mm or 3 mm, showing that a well satisfactory vibration damping material is not achieved by merely incorporating filer into the polymer matrix. Besides, WO 2002/053647 relates to a vibration damping material using a polymeric material having viscosity characteristics, in which there are exemplified polymers having the viscosity characteristics. However, there is no specific description about the starting material for constituting the polymer.
JP2003-201373 A discloses a vibration damping material in which mica is incorporated as a filler in a polymeric material. However, there is no description about a vibration damping material prepared by incorporating mica into a polyester resin or a vibration damping material specifying an average particle diameter of mica in the vibration damping material.